1. Technical Field
The present invention relates to a technology for configuring high-speed optical transmission and flexible network by using a WDM (wavelength division multiplexer) in an optical access network, and more particularly, to a WDM-PON (passive optical network) as one of the technologies for configuring an optical access network.
2. Background Art
Recently, technologies for configuring high-speed optical transmission and flexible network by using a WDM in an optical access network have been researched and developed in the world (For example, refer to Japanese Patent Application Laid-Open Publication No. 2004-222304). Among them, single longitudinal mode oscillation by performing injection locking in one of a plurality of longitudinal modes of an inexpensive FP-LD (Fabry-Perot Laser Diode) has been researched as one economical technology (For example, refer to N. Kashima and M. Watanabe, “Transient Properties of Side-Mode Injection Locking in an FPLD”, IEEE/OSA, Journal of Lightwave Technology, Vol. 24, No. 3, pp. 1523-1533, March 2006, N. Kashima, “Dynamic Properties of FP-LD Transmitters Using Side-Mode Injection Locking for LANs and WDM-PONs”, IEEE/OSA, Jounal of Lightwave Technology, Vol. 24, No. 8, pp. 3045-3058, August 2006, L. Y. Chan, et al., “Upstream traffic transmitter using injection-locked Fabry-Perot laser diode as modulator for WDM access networks”, Electronics Letters, Vol. 38, No. 1, pp. 43-45, 3 Jan. 2002, and H. D. Kim, et al., “A Low-Cost WDM Source with an ASE Injected Fabry-Perot Semiconductor Laser”, IEEE Photonics Technology Letters, Vol. 12, No. 8, pp. 1067-1069, August 2000).
FIG. 6 is a view illustrating a configuration of an example of a conventional optical transmission system. In the conventional method, since injected light (master light) is injection-locked in the FP-LD, a light having the same wavelength as the injected light is generated from the FP-LD. In such a method, a light having a wavelength λi in a direction (hereinafter, referred to as a downward direction) from a central office apparatus (hereinafter, referred to as optical line terminal) 11 to a subscriber premises apparatus (hereinafter, referred to as optical network unit) 53-i (i is an integer of 1 to N) is transmitted. The light is firstly injection-locked in the FP-LD, and then, the light is reversely transmitted from the optical network unit 53-i to the optical line terminal 11. Therefore, the uplink and downlink wavelengths become equal to λi.